The Internet essentially consists of several protocols, of which Transmission Control Protocol (TCP) and Internet Protocol (IP) are commonly used protocols. IP, for example, requires the location of any node connected to the network to be assigned a unique IP address. IP was created on the assumption that a single assigned IP address was sufficient to enable a node to access the Internet. The introduction of mobile nodes, which today include portable computers, cellular telephones, media players, and other mobile devices, introduced a challenge that IP did not address, namely, the situation when a node moves to a new physical location, it must, pursuant to IP, change its IP address. Mobile Internet Protocol (Mobile IP or MIP), among others, was created to address this challenge. Mobile IP is a standard communications protocol designed by the Internet Engineering Task Force (IETF) and enables mobile nodes to remain connected to a network regardless of their locations and without changing their respective IP addresses.
Mobile IP enables node mobility by binding the mobile node's home address to a care-of address. The home IP address and the care-of address are maintained in specialized routers called mobility agents. There are two types of mobility agents: home agents and foreign agents. The home agent is a router in a home network associated with the mobile node which maintains the mobility binding in a mobility binding table. Foreign agents are specialized routers on the foreign network visited by the mobile node. The foreign agent maintains a visitor list which contains information about the mobile nodes currently visiting that network. Typically, the care-of address is the foreign agent's IP address. Mobility agents advertise their presence and availability to mobile nodes by periodically (for instance, once every three seconds) broadcasting an IRDP (Internet Control Message Protocol (ICMP) Router Discovery Protocol) message listing one or more care-of addresses which, when received by a mobile node, may result in the mobile node requesting registration with the home agent. The mobile node receives an IRDP message from the new foreign agent in order to determine that it has roamed on a new network and before it can register with the home agent via the foreign agent. Since IRDP messages are sent periodically (e.g., every three seconds), mobile node users experience service interruptions caused by the inherent registration delays. Once an IRDP message containing the new foreign agent information is received by the mobile node, the mobile node triggers the registration with the home agent via the foreign agent. A successful Mobile IP registration sets up the routing mechanism between the home agent and the mobile node, as the mobile node roams across different networks.
Accordingly, there are problems in the registration of mobile nodes with foreign agents, for example, those that result in slow or latent IP handoffs causing a nonoptimal user experience. Many mobile nodes, such as cellular telephones, in practical use, move rapidly across the physical boundaries of foreign networks. Such mobile nodes are typically engaged in data sessions supporting a variety of user experiences, including, for instance, IP-based voice communications, or VoIP. VoIP generally requires its end-to-end delay to be lower than 250 ms, delay variance or jitter lower than 50 ms, and packet loss rate less than 1%. The currently available handoff process utilizing IRDP cannot satisfy the requirements of real-time interactive application because the communication disruption period is too long and the long communication disruption causes packet loss. Thus, a mobile node user engaged in a data session can experience service interruption or even loss of service if the mobile node moves into a new network or region area.
Further, building out an entire network using layer 2 has scalability issues such as broadcasts, multicasts and slow spanning tree convergence. Some very large layer 2 networks have been built, but eventually there is an upper limit to the number of nodes that can be deployed in the same layer 2 network. Similarly, building out the entire network using layer 3 involves latency issues due to the fact that routers do their work in software and not in hardware. An available method mixes layers 2 and 3. In practical application, approximately sixty to ninety nodes are bundled into a regional layer 2 network, or region. An intra-region handoff is via layer 2 and inter-region handoffs require both a layer 2 and a layer 3 handoff.